Yamaha CS-70m PSU / tranformer troubleshooting

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error_trials
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Yamaha CS-70m PSU / tranformer troubleshooting

Post by error_trials » Mon Aug 28, 2023 5:54 am

Welp I moved my CS-70m into a new room, and hadn't powered it on in a couple months. Flipped the power switch, lights flashed, then nothing. Won't power on now. Fuses are all ok. I had previously fixed some other issues as chronicled here and have really been loving this instrument.

I have probed around a bit, the test points (+5V, +10V, +15V, -5V and -15V) on the PSU are all way off.
With the other boards disconnected, those voltages read:
+5V test point: +3.0V
+10V test point: +8.4V
+15V test point: +17.4V
-5V test point: +1.8V
-15V test point:, +2.1V

I'm looking at the AC part of the schematic, and I don't see anywhere what the power transformer outputs are supposed to be? They measure 13.0Vac and 19.2Vac. Is this right? The AC board has only a few things on it, but I'm confused by the voltage measurements there, coming into the transformer, so if those transformer outputs are off maybe something the AC board is part of the issue.

If those are the right AC transformer output values... then I'll start looking around on the PSU, from the measurements I took it seems all the different supply voltages are messed up, so potentially several different things are causing problems.

Looking forward to playing this again, hoping I can get this PSU figured out, and then see if anything else got cooked on other boards.

Any thoughts or guidance are very much appreciated.

Thanks!!

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error_trials
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Re: Yamaha CS-70m PSU / tranformer troubleshooting

Post by error_trials » Fri Sep 08, 2023 5:51 pm

To anyone following along :mrgreen: I posted this question on another forum and have some activity... if you want to chime in you can also go here

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error_trials
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OK... Tech recommendations? :)

Post by error_trials » Fri Oct 27, 2023 4:51 pm

I've set this aside without any luck, but would love any recommendations for techs in the LA area. Most that I'm familiar with are super booked or not willing to work on this particular synth (size+weight, complexity).

Thanks!!

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